Divided conductor for electrical distributing systems.



W. H. COLE. DIVIDED CONDUCTOR FOR ELECTRICAL DISTRIBUTING SYSTEMSI APPLICATION FILED DEC. 3, 1914.

1,177,998. l .1. Patented Apr.4,1916.

IWiTnesses. I lnvenon IMM WIIIIQmHcOIe I IIYMMQM UNITED sTATEs PATENT oEEIoE.

WILLIAM H. COLE, OF WALTHAM, MASSACHUSETTS.

ffinvipnn CONDUCTOR Een E To all whom it may concern: Be it known that I, IVTLLIAM H. COLE, a citi-zen of the United` States, residing at VlValtham, county ofl\,liddlesex, State of Massachusetts;.have invented an Improvement =in Divided Conductors for Electrical Distributing Systems, of which the following description, `inuconnection with the accompanying. drawing, is a specification, like characters on the drawing representing like parts'. y

This invention relates'to conductors foi` electrical distributingsystems of that type which' might'be termed divided conductors, by which expression I mean a conductor or cable having i extending longitudinally thereof a plurality of conductor members orlea'dsl which are insulated from each other. 'It has been heretofore proposed to employ divided conductors of this construction in electrical-distributing systems with the conductor members or leads of each conductor connected in parallel and when thisl construction is used the various conductor members will normally carry current of substantially' the lsame voltage unless some means be employed to 'create a difference of potential? between them for' some special purposes.' ylVhere a divided conductor is thus used an insulation of low value is sufiicient to Vinsulate the members of any conductor from each other so long as normal conditions exist in the electrical-distributing .system because, since the conductor members are connected in parallel, they will under normal conditions carry substantially thejsame voltage or at least the difference ,of voltage betweeny the iconductor members `w il'l remain within 'fixed limits. u flvhendiv'idcd conductors as above described areused in an electrical-distributing system which has automatic disconnective devices for cutting out the conductor when .a fault occurs, which disconnective devices arevlof that type that are normally held in zbalance or inoperative bythe normal current conditions, it hasbeen thought necessary to make the` separator insulation be- 'a divided conductor ,ttwe'en' the members lof not Vonly of sufficient' Awithstan-d any .normal ,whieh1 Aexists between bei-fs, but of sufficient"additional dielectric strength to withstand the lpotential differf'enfce dueto the presence of a fault in one of Specification of Letters Patent.-

dielee'tric strength to potential difference the conductor mem-v ..theconductormembers. he reason for this i LECTRICAL DISTRIBUTING SYSTEMS.

Patented Apr. 4, 1916.

Application med December s, 1914. serial No. 875,373.V

has been because if the separator insulation was only of sullicient. dielectric strength to withstand the normal potential difference existing between the conductor members, the abnormal difference of potential which might exist between the conductor members due to the occurrence of a fault involving one of the conductor members would bel likely to cause the separator insulation to break down at the point of fault, orat some other point, either on account of the heat and burning due to arcing at the point of fault or on account of the abnormal potential dilference caused bythe fault. This breaking down of the separator insulation lwould establish an electrical connection between the conductor members, thus tending to equalize the potential in them which would prevent the unbalanced current conditi'ons in the conductors necessary to operate the disconnective devices. rl`he manufacture of divided conductors for usein an electrical-distributing system having disconnective devices and where the two conductor members are connected in parallel, has, therefore, necessitated the use ofseparator insulation having lav considerably greater dielectric strength than is necessaryV to merely withstand the normal potential difference between said conductor members.

In my co-pending application Se. No. 7 98,594, filed October 31, 1913, I have illustrated and described an electrical-distributing system involving a divided conductor and disconnective means for disconnecting the connector from the system when a fault occurs in said conductor wherein the failure of thev separator insulation between the conductor members due to a fault involving one 95 vof said members does not render the disconnective device inoperative, but, von the other hand, will cause it to operate. A divided conductor operating in a system of this nature does not require a separator insulation between the conductor members of sufficient .dielectric strength to withstand potential difference due to initial faults,'as the break downof such separator insulation does not render the system inoperative.

vThe present invention has for its object to provide a novel form of divided conductor `in which the separator insulation as a whole need onlybe commensurate with the operating, voltage required between the conductor members, and which is intentionally made weaker or of reduced value at predetermined points along the conductor, and which preferably will be of such a nature and thickness as to be readily weakened dielectrically b v the heat due to arcing at a fault. A divided conductor of this nature has special utility in a systemof electrical distribution involving' a selective disconnccting means such as shown in my said copending application Se. No. 798,594, vfor when used in such a system any break down of the separator insulation due to a fault initially affecting one conductor member only will occur either at the point of the main fault or at the predetermined weak points along the conductor or cable, which weak points will be intentionally located at readily accessible places so that repairs may be conveniently made. The advantage I gain bv theuse of. a. conductor of this nature vis that -since the separator insulation need onlv be commensurate with the operating voltage required between the conductor members, the expense of manufacture is considerably reduced.

In order to give a better understanding of mv invention, I have illustrated in the drawings a selectedembodiment thereotl which will now be described.

Figure l is a cross sectional view of a three-conductor cable embodying my inven tion; Fig. Q is a partial sectional view through the joint connecting different sections of the cable; Fig. 3 is a. more or less diagrammatic view showing a cable embodying my invention laid in an underground conduit. Fig. al. is a .diagran'nnatic view showing the application of my improved conductor in an electri al-distribut-v ing system, such as illustrated in my said co-pending application Se. No. 798,594.

Fig. 1 shows a cable for a three-phase system having a divided conductor for each phase. Each divided conductor comprises the two conductor members 3 and el which are separated bv insulation 5. conductor members are shown as arranged concentrically, that is, the member 3 is sitnated within the member 4, and the two members are inclosed in insulation 6. vThese two conductor members 3 andi are intended to be connected in parallel so that under normal conditions they Iwill carry current' ofsubstantially the same potential. There will, therefore, be comparatively little, if-

any, difference of potential between thc conductor members 8 and 4 when the conductor is in normal operation.' A divided conductor of this nature may be used singly or may be made in the form of. a multi-conductor cable, such as -tliree-conductor-cable, as

' shown in. Fig. 1.

In Fig. 4 I have shown in diagram a divlded conductor in an electrical-distributing system, such as shown in mv said co-pendii'rgna-pglication Se. No. 798,594. 30 and 31 These two designate two receiving or distributing buses or mains which are connected by a` divided conductor, the two conductor members' of which are shown at 33 and 3l, respectively. These two conductor members are connected in parallel and are connected at cach end to the buses 3() (ii-'31 through a switch device 85. This switch is arranged to be actuated to disconnect the conductor from the mains whenever a fault occurs involving either or both conductors and the disconnective device herein shown comprises a primarv winding 3G in each conductor member at each end thereof and a common secondary 3T cooperating with the two pri- Se maries at each end'. each secondary 3 7 being ina circuit 38 having a trip coil 39 therein which when energized closes contacts l() in a circuit 41 connected to a switch-operating magnet lf2 bv which the switch $35 is operated. The two conductor members 3? and 3J: are shown as transposed at a point in the length of the conductor, as shown at i3. so that the current path through the conductor is partly in thel inner and partly in the outer conductor member. A reactance #il is placed in each current path` one react-ance being situated at one' end of the" conductor and the other at the other end of! the conductor so`that`under normal conv9- ditions a dili'erence of potential will exist between the conductor members throughout the length of the conductors. lith this arrangement the transformers ateachend of the conductor will be held in balance under normal working conditions, but if a fault occurs involving either a single conductor member or both of the conductor members, the current flo-wing through the transformers will be unbalanced and the disconnective devices will be operated. It will be noted that with this arrangement any break down of the insulation between the conductor members 33 and 34 will cause the disconnective device to be operated because such break down of insulation will result in current flowing from the conductor member having a higher potential to thathaving a lower potential and thus in unbalaneing'the transformers.

It has heretofore been thought that in order to successfully use a divided conductor of Athis nature in an electrical-distributing system having` conductor-disconnectivrl devices that are normally held in balance or inoperative by balancing the current in one conductor member against that in the other,` it was necessary to make the conductor with the separator insulation between the conductor members not only of suiicient dielectric strength to withstand the normal operatingpotential difference between the conductor members, but also ofsuiiicient added dielectric strength to withstand any momentary potential difference that 'might exist should 130 leakage from` eitherV conductor member to the earth or to another lead occur, as above described. lVhere-a divided conductor is used in connection, with the disconnective 5 devices shownin Fig. 4 it is not necessary for the practical working of the system to provide such conductor with the separator insulation having the -added dielectric strength above referred to over and above that necessary to withstand the normal operating' voltage between the conductor members because in the device shown in Fig. 4:

the disconnective devices will operate to disconnect tlie conductors from the system whenever the separator insulation between the conductor members breaks down at any point sutticiently to permit current to fiow from one conductor member to the other.

It, however, a divided conductor were used in an electrical-distributing system disclosed in Fig. 4, vwhich conductor had separator insulation merely of sufficient dielectric strength to withstand the normal operating potential difference existing between the conductor members and a 'fault should occur involving either conductor member which caused an increase of potential difference between the conductor members, such increasev of potential difference would tend to break down the insulation between the conductor members either at the point of fault or at some other point. .It is, of course, desirable that in case the separator insulation is thus breken down at any point other than the point of fault, such other point shall be in an accessible location where repairs can be easily made, and my improved conductor is so constructed as to provide for this contingency and to assure that if the separator insulation does break at some point other than the point of fault it will be at predetermined locations. I secure this end by making the separator insulation of a strength throughout its length commensurate with the normal operating potential difference between theJ conductor members and also provide it with weakened places at predetermined points, so that whenever there is a tendency for such separator insulation to become ruptured u'pon the occurrence of a fault at a point other than the point of fault, such rupture will occur at the predetermined weakened points. These predetermined weakened places in the insulation may be located at any desired point along the length of the conductor. In actual practice it will probably be found most convenient to locate such places at the joints where different sections of the conductors aie connected, for these joints are usually situated in some accessible position.

In the manufacture and installation of conductors for electrical-distributing systems of considerable length, it is customary tomake and lay the conductors in sections conduit l and the ljoints and to connect the sections togetherby a n suitable joint which is usually in some rac-`A cessible position. If. for instance, the cable or conductor isy an lunderground conductor,

as shown in Fig; 3,' 'it would ybev laid inthe 70 7 between the conductor sections are'generally formed 4in ya manhole 2. .In the practical embodiment of vmy invention I proposeto make the points where the insulation between the members 3 and l of each conductor is weakest at the joint 7, and this can be readily done when the, joint is madeA by placing at the joint between the conductor members 34 and -lfinsulation of less thickness and less'value than exists between said members in tlie=body of the conductor. have shown in Fig. 2f a. typical joint connecting? the conductors. The two meeting ends ol the conductor members 3 ot' two adjacent conductorv sections are s )ldered or otherwise connected together, as shown at 9, and the meeting ends of the outer conductor members 4c are also connected or soldered together, as shown at 10. In making this joint the conductor member 4 and the insulation 5 are stripped back at the end of the conductor members and the two members 3 are soldered or joined together, as at 9, after which suitable insulation l1 is placed about the joint and the ends of the conductor member 4 are brought together and connected, the joint thus made being inclosed in exterior insulation 12 of suitable thickness. In making this joint the insulation 11 is purposely made so as to have less insulating value than the insulation 5 between the conductor members 3 and l in the body ot -the conductor so that when the conductor is completed the .insulation between the conductor members 3 and l will be weakest at the points 11. 'lhe advantage of this construction is that it during the development of a fault a pressure or. potential is developed between the conductor members 3 and 4 which is suliicient to puncture or destroy the insulation 5, this pressure will, unless the heating of the separatoi' insulation at the place of the fault causes puncture at that point, cause the insulation to give way at the weaker point 11 which is at the joint where it can be readily repaired instead of at some indeterminate point between the ends of the conductor sections. .It the insulationA should give way at some indeterminate point this would necessitate pulling the entirev cable out from the conduit in order to effect a repair.

My invention` therefore, provides a construction which insures that in case the vseparator insulation breaks down at any. point other than the point of fault, such break down will occur at'some readily-accessible point.

It is desirable to use a separator insulation ot such a. nature and thickness as will be readily weakened dielectrically by the heat due to the arcing at a fault, and while any insulation having this feature may be used I nd that insulation made of varnished eotton or similar fabric will meet all these reqnirements.

I claim:

1. A conductor comprising a pair of conduetor membersor leads and insulating means between said members which is com mensurate vwith the normal operating voltage employed between said members when they are connected in pa allel in an electrical-distributing system. said insulating means being weaker at predetermined points along the length of the conductor whereby when a fault occurs that develops unsafe voltage between said members the insulation will give way at the predetermined point.

A conductor comprising a pair ot' conductor members and insulating means between saidf conductor members for insulating one from the other, which means has at predetermined points a less/dielectric strength than at other points.

3. A conductor comprising a pair of parallel-connected leads separated by insulation commensurate at all points with the normal working voltage between said leads, said insulation at predetermined points having a less dielectric strength than the normal strength throughout the body ot' the insulation.

l. A conductor comprising a pair of parallel-connected leads separated b v insulation commensurate at all points with the normal working voltage between said leads, said insulation having the characteristic of being readily weakened dielectricallv by the heat due to an are resulting Jfrom a fault and at predetermined points having a less dielectric strength than the normal strength throughout the body of the insulation.

In testimony whereof, I have signed my name to this specification. in the presence of two subscribing witnesses. v

WILLIAM H. COLE.

lvitnesses BERTHA I". I-IEUsER, THowAs J. DRUMMOND.

Copies of this patent may be obtained for ve cents each, by addressing the Commissioner of latents,

Washington, n. c.V 

